The proposed research is designed to systematically explore the host-parasite relationships in the pregnant woman. Specifically, we will investigate the possible modulating effects of pregnancy and female sex hormones on the biochemical and antimicrobial activities of phagocytes collected from human and animal models and from pregnant animals and humans. More specifically, we will study: 1) the basic biochemical and antimicrobial mechanisms involved in the myeloperoxidase (MPO)-H2O2-C1- system so that its precise function in the pregnant state can be elucidated; 2) biological effects of estrogens on halide dependent peroxidase antimicrobial activity; 3) the significance of amniotic fluid peroxidases and their relationships to fetal well-being; 4) the relationships of AF peroxidase and relevant microorganisms including mycoplasma and chlamydia.